1. Field of the Invention
The present invention relates to an improved process for producing a styrenic polymer. More particularly it pertains to a process for producing a styrenic polymer which has high degree of syndiotactic configuration and a wide range of molecular weight distribution and is reduced in residual metallic components at a low production cost with a high efficiency.
2. Description of Related Art
There have heretofore been known the processes for producing high-performance styrenic polymer having high degree of syndiotactic configuration in high yield by allowing a reaction product of an aluminoxane with a transition metal complex to act on styrene. (Refer to Japanese Patent Application Laid-Open Nos. 187708/1987, 179906/1988, 241009/1988, etc.). However, the styrenic polymer produced by any of the above-disclosed processes involves the problem of moldability due to the usually narrow range of molecular weight distribution. Accordingly there is desired a styrenic polymer which has high degree of syndiotactic configuration and besides a wide range of molecular weight distribution.
In order to produce such a styrenic polymer having a wide range of molecular weight distribution, there has heretofore been employed a method in which a high molecular styrenic polymer and a low molecular styrenic polymer are mixed with each other by melt kneading or the like to expand the range of molecular weight distribution. However, the aforesaid method involves the problem of requiring much labor and effort for uniform mixing.
There is also known a method of expanding the molecular weight distribution by the use of a plurality of transition metal compounds and an aluminoxane. (Refer to Japanese Patent Application Laid-Open No. 119006/1991). Nevertheless the above-mentioned method suffers the disadvantage that a large requirement of an aluminoxane increases the catalyst cost and the amount of residual metallic components is excessive making it unserviceable unless deashing is put into practice.
Under such circumstances it is an object of the present invention to provide a process for producing a styrenic polymer which has high degree of syndiotactic configuration and a wide range of molecular weight distribution and is reduced in residual metallic components at a low production cost with a high efficiency.